Ventilation is an important part of roof design. Conventional eave ventilation is made from sheets of metal stamped with vents cut and shaped to allow air to pass through. The installation of these metal vents is expensive and time consuming because these vents have to be added after the eave is built or requires special material built into the sheathing. Additionally, the metal vent does not connect with the air passage way that is often installed as a chute made form impermeable sheets of plastic.
Moreover, ice dams are created when heat escapes from the living area or is passed through conduction to the attic. The heat then warms the surface of the roof and melts any snow that might accumulate. The interior warmth is exacerbated warming the area at the edge of the roof. The area just above is a little colder. That creates a dam at the edge of the roof. The gutter accumulates water, which results in another cold area. The space between warms the snow to a liquid and traps it. This trapped water can lead back into the occupied space.
Finally, conventional roofing design includes installing a membrane under the shingles. The membrane prevents moisture from entering the living space if moisture breaches the shingles. The membrane is typically made from bitumen or butyl rubber sheets. The membrane typically has a film on the top layer but the film must not be slippery since people walk on top of it on the roof.